Sampling device for teoi mode in



Dec. 6, 1960 L. B. FELSEN ErAL 6 6 SAMPLING DEVICE FOR TE MODE INCIRCULAR WAVEGUIDES Filed Dec. 20. 1957 INVENTORS LEOPOLD B. FELSENWALTER KU? KAHN ATI'ORNEY United States Patent SAMPLING DEVICE FOR 'I'EMODE IN CIRCULAR WAVEGUIDES Leopold B. Felsen, Flushing, and Walter KurtKahn, Brooklyn, N.Y., assignors to Polytechnic Institute of Brooklyn,Brooklyn, N.Y., a corporation of New York Filed Dec. 20, 1957, Ser. No.704,039

7 Claims. (Cl. 333-9) This invention is concerned with a slotted-sectionor wave-sampling device for use in a circular waveguide in which waveenergy is transmitted according to the circular TE mode. Theslotted-section according to this invention is useful generally for thesame purposes as the conventional slotted-section for rectangularwaveguides.

Heretofore, when it has been desired to measure energy transmitted alonga circular waveguide according to the circular TE mode, a rectangularslotted-section was inserted in the circular guide, the input end of therectangular section being connected to the circular guide through atapered guide section which converted the circular TE mode to therectangular TE mode, and the output end of the rectangular section wasconnected to the outgoing section of the circular guide through atapered section which converted the rectangular TE mode back to thecircular TE mode. The present invention provides a slotted section whichdoes not employ a rectangular waveguide section and does not re quireconversion from one mode to another.

A preferred embodiment of the invention is illustrated in theaccompanying drawing in which Figure 1 is a side view of a circularwaveguide section, embodying the invention, and Figures 1a, 1b, 1c, and1d are sectional views of Figure 1 taken along the transverse planes ato d, respectively. The wall thicknesses are exaggerated in the drawing.

As shown in Figure 1, the slotted-section of this invention is embodiedin a section of circular waveguide which is of circular section at bothends and may be provided with conventional coupling flanges forinsertion into a transmission line of circular section. The wall of thecircular waveguide section is indented or otherwise formed to provide anelongated trough formed lengthwise of the section and having planarsidewalls joined along their inner edges at the axis of the section.Thus, as shown in Figure la, the wall 1 of the waveguide is indented toform a trough 'having flat sidewalls 2 and 3 extending from the centerof the circular waveguide outwardly along radial lines at an angle 0. Toreduce wave reflection, both ends of the trough are tapered to a fineedge as will be seen from the sectional views shown in Figures lb, 1cand 1d, it being understood that the two ends of the trough aresymmetrically formed about the transverse mid-plane of the trough. Asshown in the drawing, it is preferred to form the trough with the wall 3remaining fiat throughout its length while the wall 2 is curved over itsend portions so that the angle between the two walls gradually decreasesuntil wall 2 merges with the wall 3 at the ends of the trough.

The wall 3 is provided with a slot 4 formed therein parallel with theaxis of the guide section, and a probe 5 extends through this slot andis suitably mounted to be moved lengthwise of the slot. This slot islocated at a position where the currents in wall 3 are purelylongitudinal. This condition is satisfied if the slot is 2,953,662Patented Dec. 6, 1960 spaced from the axis of the section by a distanceequal to 0.628 of the radius of the circular section.

Any suitable arrangement may be provided for mounting probe 5 to bemoved along this length of slot 4. For example, the probe may besupported at the end of a co-axial cable 6 which is supported on a slide7 mounted to slide on a rail 8 which is arranged parallel with the slot.

The trough formed by the walls 2 and 3 constitutes a cavity within thecircular waveguide having the shape of a cylindrical sector which isclosed at both ends. The angle 6 of the sector, the angle between theflat portions of walls 2 and 3, should be just sulficient to permit themounting of the probe for movement within the slot 4. The end tapers forthe trough can then be short by comparison with tapers of equal qualityfor converting from circular TE mode to rectangular TE mode. Roughly,the ratio of taper lengths in the two cases would be 0/ 211-.

With the arrangement described above, the probe 5 extends through theslot in the wall 3 in a direction parallel with the electric field ofthe wave energy for the circular TE mode, and the probe will respond towave energy in the same manner as in the case of a slotted-section ofrectangular waveguide.

For the purpose of reducing or suppressing spurious modes which might beexcited by the probe, a thin radial wall or fin 9 is mounted in the mainguide to form a sampling guide between the wall 3 and the fin 9. Thus,the probe 5 extends into a sectoral sampling guide of small angle whichis open at both ends to the main guide. Excitation of spurious modes andreflections can occur only where the main guide and sampling guiderejoin and would be due to transmission phase or amplitude diflerencesbetween these two guides. The phase difierences can be compensated, theamplitude differences cannot be compensated, and must be kept small,i.e., the probe must be lightly coupled.

From the foregoing it will be seen that the invention provides awave-sampling device in which the probe 5 extends through a longitudinalslot formed in a flat plate 3 arranged radially within the circularwaveguide section, the probe extending through the slot in a directionparallel with the electric field for the TE mode and the probe beingmounted for movement lengthwise of the slot. The radial plate 9 need notbe used except where it is desired to prevent spurious modes developedby the probe. The radial wall 2 is provided to shield the probe and itsmounting from wave energy transmitted on the opposite side of plate 3from the plate 9 and thereby prevent wave reflection from the shieldedparts. The cavity formed by the walls 2 and 3 may be closed if desiredexcept for a slot through which the co-axial cable 6 would extend.

We claim:

1. A wave sampling device comprising a section of circular waveguidehaving circular end portions and a central portion having a V-shapedtrough-like cavity formed in the wall thereof parallel with the axis ofsaid section, the walls of said cavity being formed throughout the majorportion of the length of said trough as flat walls extending in radialplanes from the axis of said section to the cylindrical wall thereof,one of said flat walls being provided with a slot formed in themidportion thereof parallel with the axis of said section, a probelocated in said cavity and extending through said slot in a directiontangent to the electric field within said section for the TE mode, andmeans mounting said probe for movement along the length of said slot.

2. A wave sampling device according to claim 1 and including a thin flatmetallic vane mounted in said section along a radial plane displaced byan acute angle from said slotted wall to form a sector-shaped samplingguide for wave energy to be sampled by said probe.

3. A wave-sampling device comprising a section of circular waveguidehaving circular end portions, meansforming a sector-shaped cavityextending longitudinally within the mid-portion of said section andcovering a small angular portion of the transverse area of said-section,said'cavity being closed at its ends by tapered end portions to preventwave reflection within said section, one radial wall of saidsector-shaped cavity being a' flat, wall extending from the axis of saidsection to the cylindrical wall thereof and having a slot formed in themidportion thereof parallel with. the axis of said section, a samplingprobe mounted within said cavity and having anend extending through saidslot in a directiontangent to the electric field for the T15 mode withinsaid section, and means mounting saidprobe for movement lengthwise oisaid slot;

4. A wave-sampling device comprising a section of circular Waveguidehaving circular end.- portions, means forming a sector-shapedsampling'guide extending longitudinally Within the middleportion of saidsection and covering a small angular portion of the transverse area ofsaid section, said sampling guide being open at its ends 'to Wave energytransmitted through said section, one of the radial wallsof saidsampling guide having;

a slot formed in the mid-portion thereof parallel with the axis of saidsection, a probe mounted outside of said sampling guide and extendinginto said slot, means supporting said probe for movement lengthwise ofsaidslot, and means within said sec-tion for shielding said probe. andits mounting means from wave energy transmitted through said mid-portionon the outside of said sampling guide.

5. A wave-sampling device comprising a section of circular waveguidehaving circular end portions, a flat Wall extending longitudinallywithin the: middlev portion of said section and extending inwardly fromthe outer wall thereof toward the center of said middle prtion, saidflat wall having a slot formed in the mid- 7 portion thereof parallelwith the axis of said section,

a probe mounted on one side of said flat wall and extending into saidslot, means supporting said probe for movement lengthwise of said slot,and means Within said section for shielding said probe and its mountingmeans from wave energy transmitted through the middle portion of saidsection on said one side of said flat wall.

6. A wave-sampling device according toclaim 5 and including a secondflat wall mounted in said section along a radial plane displaced byanacute angle from said slotted wall to. form a sector-shaped samplingguide for waveenergy to be sampledby said probe.

7. A wave-sampling device comprising a section of circular waveguidehaving circular end portions, means forming a sector-shaped sampling:guideiextendingrlongitudinally within the middle portion of said sectionand covering a small angular portion of the transverse area of saidsection, said sampling, guide being open at its end to wave energytransmitted through said section, one of theradial walls of saidsampling guide having a slot formed in the mid-portion thereof parallelwith the axis of said section, a probe mounted outsidezofsaid samplingguide Within a sector-shaped cavity extending longitudinally within themid-portion of said section and covering a small angular portion of thetransverse area of said section, said cavity being closed at its ends bytapered end portions to prevent wave reflections at the ends of saidcavity section, the slotted radial Wall of said sampling guide benig incommon with the sampling guide and thesector-shaped cavity, and meansmounting the said probe to extend through the slot into said samplingguide and for movement along the length of said slot.

References Cited in the file of this patent V UNITED STATES PATENTS2,129,714 Southworth Sept. '13, 1938 2,419,208 Frantz et al. Apr. 22,1947 2,848,690 Miller Aug. 19, 1958 2,864,063" Felsen et a1. Dec. 9,1958

